Placeholder in --gdk-debug=FLAGS in --help output
Placeholder in --gdk-no-debug=FLAGS in --help output
Placeholder in --gtk-debug=FLAGS in --help output
Placeholder in --gtk-no-debug=FLAGS in --help output

Current
Lojban:

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Located in
gdk/gdk.c:244 gdk/gdk.c:247 gtk/gtkmain.c:470 gtk/gtkmain.c:473